This invention pertains to vacuum arc switching devices and more particularly to such devices employing shielding for protecting the interior surfaces of the device from arc radiation.
In devices of the kind described high arc voltages have been obtained. By disposing an impedance in parallel across these devices it is possible to limit the fault current in high-voltage AC circuits. The arc voltage has been increased to high levels by application of an externally applied magnetic field transverse to the electrode gap. Nevertheless, other problems still exist. For example, after the arc is swept from the inter-electrode region under the influence of the magnetic field the discharge seems to continue along the ceramic wall of the vacuum enclosure with subsequent transfer to the electrode stems and/or to the metal end plates thereby coating the side walls, electrode stems and end plates with electrode material. Such coating causes rapid degradation of the device. It is therefore important to prevent such coating of the vacuum device with electrode material. This will not only prevent arc transfer but will also stop the rapid degradation of the device that occurs once the arc has burned along the ceramic wall.